427 lines
17 KiB
C
427 lines
17 KiB
C
/*
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* Copyright (C) 2013-2022 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
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* Copyright (C) 2011-2013 Sourcefire, Inc.
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*
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* Authors: Tomasz Kojm <tkojm@clamav.net>, Aldo Mazzeo, Micah Snyder
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
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* MA 02110-1301, USA.
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*/
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/*
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* GIF Format
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* ----------
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*
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* 1. Signature: 3 bytes ("GIF")
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*
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* 2. Version: 3 bytes ("87a" or "89a")
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*
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* 3. Logical Screen Descriptor: 7 bytes (see `struct gif_screen_descriptor`)
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* (Opt.) Global Color Table: n bytes (defined in the Logical Screen Descriptor flags)
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*
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* 4. All subsequent blocks are precededed by the following 1-byte labels...
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*
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* 0x21: Extension Introducer
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* 0x01: Opt. (0+) Plain Text Extension
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* 0xF9: Opt. (0+) Graphic Control Extension
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* 0xFE: Opt. (0+) Comment Extension
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* 0xFF: Opt. (0+) Application Extension
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*
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* Note: Each extension has a size field followed by some data. After the
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* data may be a series of sub-blocks, each with a block size.
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* If there are no more sub-blocks, the size will be 0x00, meaning
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* there's no more blocks.
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* The Graphic Control Extension never has any sub-blocks.
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*
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* 0x2C: Image Descriptor (1 per image, unlimited images)
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* (Opt.) Local Color Table: n bytes (defined in the Image Descriptor flags)
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* (Req.) Table-based Image Data Block*
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*
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* Note: Each image a series of data blocks of size 0-255 bytes each where
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* the first byte is the size of the data-block.
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* If there are no more data-blocks, the size will be 0x00, meaning
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* there's no more data.
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*
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* 0x3B: Trailer (1 located at end of data stream)
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*
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* Reference https://www.w3.org/Graphics/GIF/spec-gif89a.txt for the GIF spec.
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*/
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#if HAVE_CONFIG_H
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#include "clamav-config.h"
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#endif
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#include <math.h>
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#include <stdbool.h>
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#include "gif.h"
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#include "scanners.h"
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#include "clamav.h"
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/* clang-format off */
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#ifndef HAVE_ATTRIB_PACKED
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#define __attribute__(x)
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#endif
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#ifdef HAVE_PRAGMA_PACK
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#pragma pack(1)
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#endif
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#ifdef HAVE_PRAGMA_PACK_HPPA
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#pragma pack 1
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#endif
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/**
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* @brief Logical Screen Descriptor
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*
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* This block immediately follows the "GIF89a" magic bytes
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* Flags contains packed fields which are as follows:
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* Global Color Table Flag - 1 Bit
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* Color Resolution - 3 Bits
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* Sort Flag - 1 Bit
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* Size of Global Color Table - 3 Bits
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*/
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struct gif_screen_descriptor {
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uint16_t width;
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uint16_t height;
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uint8_t flags;
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uint8_t bg_color_idx;
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uint8_t pixel_aspect_ratio;
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} __attribute__((packed));
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#define GIF_SCREEN_DESC_FLAGS_MASK_HAVE_GLOBAL_COLOR_TABLE 0x80 /* If set, a Global Color Table will follow the Logical Screen Descriptor */
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#define GIF_SCREEN_DESC_FLAGS_MASK_COLOR_RESOLUTION 0x70 /* Number of bits per primary color available to the original image, minus 1. */
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#define GIF_SCREEN_DESC_FLAGS_MASK_SORT_FLAG 0x08 /* Indicates whether the Global Color Table is sorted. */
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#define GIF_SCREEN_DESC_FLAGS_MASK_SIZE_OF_GLOBAL_COLOR_TABLE 0x07 /* If exists, the size = 3 * pow(2, this_field + 1), or: 3 * (1 << (this_field + 1)) */
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/**
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* @brief Graphic Control Extension
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*
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*/
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struct gif_graphic_control_extension {
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uint8_t block_size;
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uint8_t flags;
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uint16_t delaytime;
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uint8_t transparent_color_idx;
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uint8_t block_terminator;
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} __attribute__((packed));
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/**
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* @brief Image Descriptor
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*
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* Flags contains packed fields which are as follows:
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* Local Color Table Flag - 1 Bit
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* Interlace Flag - 1 Bit
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* Sort Flag - 1 Bit
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* Reserved - 2 Bits
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* Size of Local Color Table - 3 Bits
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*/
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struct gif_image_descriptor {
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uint16_t leftpos;
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uint16_t toppos;
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uint16_t width;
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uint16_t height;
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uint8_t flags;
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} __attribute__((packed));
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#define GIF_IMAGE_DESC_FLAGS_MASK_HAVE_LOCAL_COLOR_TABLE 0x80 /* If set, a Global Color Table will follow the Logical Screen Descriptor */
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#define GIF_IMAGE_DESC_FLAGS_MASK_IS_INTERLACED 0x40 /* Indicates if the image is interlaced */
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#define GIF_IMAGE_DESC_FLAGS_MASK_SORT_FLAG 0x20 /* Indicates whether the Local Color Table is sorted. */
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#define GIF_IMAGE_DESC_FLAGS_MASK_SIZE_OF_LOCAL_COLOR_TABLE 0x07 /* If exists, the size = 3 * pow(2, this_field + 1), or: 3 * (1 << (this_field + 1)) */
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/* Main labels */
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#define GIF_LABEL_EXTENSION_INTRODUCER 0x21
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#define GIF_LABEL_GRAPHIC_IMAGE_DESCRIPTOR 0x2C
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#define GIF_LABEL_SPECIAL_TRAILER 0x3B
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/* Extension labels (found after the Extension Introducer) */
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#define GIF_LABEL_GRAPHIC_PLAIN_TEXT_EXTENSION 0x01
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#define GIF_LABEL_CONTROL_GRAPHIC_CONTROL_EXTENSION 0xF9
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#define GIF_LABEL_SPECIAL_COMMENT_EXTENSION 0xFE
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#define GIF_LABEL_SPECIAL_APP_EXTENSION 0xFF
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#define GIF_BLOCK_TERMINATOR 0x00 /* Used to indicate end of image data and also for end of extension sub-blocks */
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#ifdef HAVE_PRAGMA_PACK
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#pragma pack()
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#endif
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#ifdef HAVE_PRAGMA_PACK_HPPA
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#pragma pack
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#endif
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/* clang-format on */
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cl_error_t cli_parsegif(cli_ctx *ctx)
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{
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cl_error_t status = CL_SUCCESS;
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bool parse_error = false;
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fmap_t *map = NULL;
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size_t offset = 0;
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const char *signature = NULL;
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char version[4];
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struct gif_screen_descriptor screen_desc;
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size_t global_color_table_size = 0;
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bool have_image_data = false;
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cli_dbgmsg("in cli_parsegif()\n");
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if (NULL == ctx) {
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cli_dbgmsg("GIF: passed context was NULL\n");
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status = CL_EARG;
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goto done;
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}
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map = ctx->fmap;
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/*
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* Skip the "GIF" Signature and "87a" or "89a" Version.
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*/
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if (NULL == (signature = fmap_need_off(map, offset, strlen("GIF")))) {
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cli_dbgmsg("GIF: Can't read GIF magic bytes, not a GIF\n");
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goto done;
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}
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offset += strlen("GIF");
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if (0 != strncmp("GIF", signature, 3)) {
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cli_dbgmsg("GIF: First 3 bytes not 'GIF', not a GIF\n");
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goto done;
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}
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if (3 != fmap_readn(map, &version, offset, strlen("89a"))) {
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cli_dbgmsg("GIF: Can't read GIF format version, not a GIF\n");
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goto done;
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}
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offset += strlen("89a");
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version[3] = '\0';
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cli_dbgmsg("GIF: Version: %s\n", version);
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/*
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* Read the Logical Screen Descriptor
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*/
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if (fmap_readn(map, &screen_desc, offset, sizeof(screen_desc)) != sizeof(screen_desc)) {
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cli_errmsg("GIF: Can't read logical screen description, file truncated?\n");
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status = cli_append_potentially_unwanted(ctx, "Heuristics.Broken.Media.GIF.TruncatedScreenDescriptor");
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parse_error = true;
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goto scan_overlay;
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}
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offset += sizeof(screen_desc);
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cli_dbgmsg("GIF: Screen Size: %u width x %u height.\n",
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le16_to_host(screen_desc.width),
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le16_to_host(screen_desc.height));
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if (screen_desc.flags & GIF_SCREEN_DESC_FLAGS_MASK_HAVE_GLOBAL_COLOR_TABLE) {
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global_color_table_size = 3 * (1 << ((screen_desc.flags & GIF_SCREEN_DESC_FLAGS_MASK_SIZE_OF_GLOBAL_COLOR_TABLE) + 1));
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cli_dbgmsg("GIF: Global Color Table size: %zu\n", global_color_table_size);
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if (offset + (size_t)global_color_table_size > map->len) {
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cli_errmsg("GIF: EOF in the middle of the global color table, file truncated?\n");
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status = cli_append_potentially_unwanted(ctx, "Heuristics.Broken.Media.GIF.TruncatedGlobalColorTable");
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parse_error = true;
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goto scan_overlay;
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}
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offset += global_color_table_size;
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} else {
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cli_dbgmsg("GIF: No Global Color Table.\n");
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}
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while (1) {
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uint8_t block_label = 0;
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/*
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* Get the block label
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*/
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if (fmap_readn(map, &block_label, offset, sizeof(block_label)) != sizeof(block_label)) {
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if (have_image_data) {
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/* Users have identified that GIF's lacking the image trailer are surprisingly common,
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can be rendered, and should be allowed. */
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cli_dbgmsg("GIF: Missing GIF trailer, slightly (but acceptably) malformed.\n");
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} else {
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cli_errmsg("GIF: Can't read block label, EOF before image data. File truncated?\n");
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status = cli_append_potentially_unwanted(ctx, "Heuristics.Broken.Media.GIF.MissingImageData");
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}
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parse_error = true;
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goto scan_overlay;
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}
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offset += sizeof(block_label);
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if (block_label == GIF_LABEL_SPECIAL_TRAILER) {
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/*
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* Trailer (end of data stream)
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*/
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cli_dbgmsg("GIF: Trailer (End of stream)\n");
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goto scan_overlay;
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}
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switch (block_label) {
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case GIF_LABEL_EXTENSION_INTRODUCER: {
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uint8_t extension_label = 0;
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cli_dbgmsg("GIF: Extension introducer:\n");
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if (fmap_readn(map, &extension_label, offset, sizeof(extension_label)) != sizeof(extension_label)) {
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cli_errmsg("GIF: Failed to read the extension block label, file truncated?\n");
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status = cli_append_potentially_unwanted(ctx, "Heuristics.Broken.Media.GIF.TruncatedExtension");
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parse_error = true;
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goto scan_overlay;
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}
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offset += sizeof(extension_label);
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if (extension_label == GIF_LABEL_CONTROL_GRAPHIC_CONTROL_EXTENSION) {
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cli_dbgmsg("GIF: Graphic control extension!\n");
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/* The size of a graphic control extension block is fixed, we can skip it quickly */
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offset += sizeof(struct gif_graphic_control_extension);
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} else {
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switch (extension_label) {
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case GIF_LABEL_GRAPHIC_PLAIN_TEXT_EXTENSION:
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cli_dbgmsg("GIF: Plain text extension\n");
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break;
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case GIF_LABEL_SPECIAL_COMMENT_EXTENSION:
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cli_dbgmsg("GIF: Special comment extension\n");
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break;
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case GIF_LABEL_SPECIAL_APP_EXTENSION:
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cli_dbgmsg("GIF: Special app extension\n");
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break;
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default:
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cli_dbgmsg("GIF: Unfamiliar extension, label: 0x%x\n", extension_label);
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}
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while (1) {
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/*
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* Skip over the extension and any sub-blocks,
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* Try to read the block size for each sub-block to skip them.
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*/
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uint8_t extension_block_size = 0;
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if (fmap_readn(map, &extension_block_size, offset, sizeof(extension_block_size)) != sizeof(extension_block_size)) {
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cli_errmsg("GIF: EOF while attempting to read the block size for an extension, file truncated?\n");
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status = cli_append_potentially_unwanted(ctx, "Heuristics.Broken.Media.GIF.TruncatedExtension");
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parse_error = true;
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goto scan_overlay;
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} else {
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offset += sizeof(extension_block_size);
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}
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if (extension_block_size == GIF_BLOCK_TERMINATOR) {
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cli_dbgmsg("GIF: No more sub-blocks for this extension.\n");
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break;
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} else {
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cli_dbgmsg("GIF: Found sub-block of size %d\n", extension_block_size);
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}
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if (offset + (size_t)extension_block_size > map->len) {
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cli_errmsg("GIF: EOF in the middle of a graphic control extension sub-block, file truncated?\n");
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status = cli_append_potentially_unwanted(ctx, "Heuristics.Broken.Media.GIF.TruncatedExtensionSubBlock");
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parse_error = true;
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goto scan_overlay;
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}
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offset += extension_block_size;
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}
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}
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break;
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}
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case GIF_LABEL_GRAPHIC_IMAGE_DESCRIPTOR: {
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struct gif_image_descriptor image_desc;
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size_t local_color_table_size = 0;
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cli_dbgmsg("GIF: Found an image descriptor.\n");
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if (fmap_readn(map, &image_desc, offset, sizeof(image_desc)) != sizeof(image_desc)) {
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cli_errmsg("GIF: Can't read image descriptor, file truncated?\n");
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status = cli_append_potentially_unwanted(ctx, "Heuristics.Broken.Media.GIF.TruncatedImageDescriptor");
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parse_error = true;
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goto scan_overlay;
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} else {
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offset += sizeof(image_desc);
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}
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cli_dbgmsg("GIF: Image size: %u width x %u height, left pos: %u, top pos: %u\n",
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le16_to_host(image_desc.width),
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le16_to_host(image_desc.height),
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le16_to_host(image_desc.leftpos),
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le16_to_host(image_desc.toppos));
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if (image_desc.flags & GIF_IMAGE_DESC_FLAGS_MASK_HAVE_LOCAL_COLOR_TABLE) {
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local_color_table_size = 3 * (1 << ((image_desc.flags & GIF_IMAGE_DESC_FLAGS_MASK_SIZE_OF_LOCAL_COLOR_TABLE) + 1));
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cli_dbgmsg("GIF: Found a Local Color Table (size: %zu)\n", local_color_table_size);
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offset += local_color_table_size;
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} else {
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cli_dbgmsg("GIF: No Local Color Table.\n");
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}
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/*
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* Parse the image data.
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*/
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offset++; /* Skip over the LZW Minimum Code Size uint8_t */
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while (1) {
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/*
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* Skip over the image data block(s).
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* Try to read the block size for each image data sub-block to skip them.
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*/
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uint8_t image_data_block_size = 0;
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if (fmap_readn(map, &image_data_block_size, offset, sizeof(image_data_block_size)) != sizeof(image_data_block_size)) {
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cli_errmsg("GIF: EOF while attempting to read the block size for an image data block, file truncated?\n");
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status = cli_append_potentially_unwanted(ctx, "Heuristics.Broken.Media.GIF.TruncatedImageDataBlock");
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parse_error = true;
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goto scan_overlay;
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} else {
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offset += sizeof(image_data_block_size);
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}
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if (image_data_block_size == GIF_BLOCK_TERMINATOR) {
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cli_dbgmsg("GIF: No more data sub-blocks for this image.\n");
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break;
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} else {
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cli_dbgmsg("GIF: Found a sub-block of size %d\n", image_data_block_size);
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}
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if (offset + (size_t)image_data_block_size > map->len) {
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cli_errmsg("GIF: EOF in the middle of an image data sub-block, file truncated?\n");
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status = cli_append_potentially_unwanted(ctx, "Heuristics.Broken.Media.GIF.TruncatedImageDataBlock");
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parse_error = true;
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goto scan_overlay;
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}
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offset += image_data_block_size;
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}
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have_image_data = true;
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break;
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}
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default: {
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// An unknown code: break.
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cli_errmsg("GIF: Found an unfamiliar block label: 0x%x\n", block_label);
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status = cli_append_potentially_unwanted(ctx, "Heuristics.Broken.Media.GIF.UnknownBlockLabel");
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parse_error = true;
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goto scan_overlay;
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}
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}
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}
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scan_overlay:
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if (CL_SUCCESS == status) {
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if (parse_error) {
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// Some recovery (I saw some "GIF89a;" or things like this)
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if (offset == (strlen("GIF89a") + sizeof(screen_desc) + 1)) {
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offset = strlen("GIF89a");
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}
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}
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// Is there an overlay?
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if (offset < map->len) {
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cli_dbgmsg("GIF: Found extra data after the end of the GIF data stream: %zu bytes, we'll scan it!\n", map->len - offset);
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status = cli_magic_scan_nested_fmap_type(map, offset, map->len - offset, ctx, CL_TYPE_ANY, NULL, LAYER_ATTRIBUTES_NONE);
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goto done;
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}
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}
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done:
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return status;
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}
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